Method and system for design of a reticle to be manufactured using character projection lithography

ABSTRACT

A method for fracturing or mask data preparation or proximity effect correction is disclosed which comprises the steps of inputting patterns to be formed on a surface, a subset of the patterns being slightly different variations of each other and selecting a set of characters some of which are complex characters to be used to form the number of patterns, and reducing shot count or total write time by use of a character varying technique. A system for fracturing or mask data preparation or proximity effect correction is also disclosed.

BACKGROUND OF THE DISCLOSURE

The present disclosure is related to lithography, and more particularlyto the design and manufacture of a surface which may be a reticle, awafer, or any other surface, using character or cell projectionlithography.

In the production or manufacturing of semiconductor devices, such asintegrated circuits, optical lithography may be used to fabricate thesemiconductor devices. Optical lithography is a printing process inwhich a lithographic mask or reticle is used to transfer patterns to asubstrate such as a semiconductor or silicon wafer to create theintegrated circuit. Other substrates could include flat panel displaysor even photomasks. Also, extreme ultraviolet (EUV) or X-ray lithographyare considered types of optical lithography. The reticle or multiplereticles may contain a circuit pattern corresponding to an individuallayer of the integrated circuit and this pattern can be imaged onto acertain area on the substrate that has been coated with a layer ofradiation-sensitive material known as photoresist or resist. Once thepatterned layer is transferred the layer may undergo various otherprocesses such as etching, ion-implantation (doping), metallization,oxidation, and polishing. These processes are employed to finish anindividual layer in the substrate. If several layers are required, thenthe whole process or variations thereof will be repeated for each newlayer. Eventually, a combination of multiples of devices or integratedcircuits will be present on the substrate. These integrated circuits maythen be separated from one another by dicing or sawing and then may bemounted into individual packages. In the more general case, the patternson the substrate may be used to define artifacts such as display pixelsor magnetic recording heads.

In the production or manufacturing of semiconductor devices, such asintegrated circuits, maskless direct write may also be used to fabricatethe semiconductor devices. Maskless direct write is a printing processin which patterns are transferred to a substrate such as a semiconductoror silicon wafer to create the integrated circuit. Other substratescould include flat panel displays, imprint masks for nano-imprinting, oreven photomask. Desired patterns of a layer are written directly on thesurface, which in this case is also the substrate. Once the patternedlayer is transferred the layer may undergo various other processes suchas etching, ion-implantation (doping), metallization, oxidation, andpolishing. These processes are employed to finish an individual layer inthe substrate. If several layers are required, then the whole process orvariations thereof will be repeated for each new layer. Some of thelayers may be written using optical lithography while others may bewritten using maskless direct write to fabricate the same substrate.Eventually, a combination of multiples of devices or integrated circuitswill be present on the substrate. These integrated circuits are thenseparated from one another by dicing or sawing and then mounted intoindividual packages. In the more general case, the patterns on thesurface may be used to define artifacts such as display pixels ormagnetic recording heads.

As indicated, the lithographic mask or reticle comprises geometricpatterns corresponding to the circuit components to be integrated onto asubstrate. The patterns used to manufacture the reticle may be generatedutilizing CAD (computer-aided design) software or programs. In designingthe patterns the CAD program may follow a set of predetermined designrules in order to create the reticle. These rules are set by processing,design, and end-use limitations. An example of an end-use limitation isdefining the geometry of a transistor in a way in which it cannotsufficiently operate at the required supply voltage. In particular,design rules can define the space tolerance between circuit devices orinterconnect lines. The design rules are, for example, used to ensurethat the circuit devices or lines do not interact with one another in anundesirable manner. For example, the design rules are used so that linesdo not get too close to each other in a way that may cause a shortcircuit. The design rule limitations reflect, among other things, thesmallest dimensions that can be reliably fabricated. When referring tothese small dimensions, one usually introduces the concept of a criticaldimension. There are, for instance, defined as the smallest width of aline or the smallest space between two lines, these dimensions requiringexquisite control.

One goal in integrated circuit fabrication by optical lithography is toreproduce the original circuit design on the substrate by use of thereticle. Integrated circuit fabricators are always attempting to use thesemiconductor wafer real estate as efficiently as possible. Engineerskeep shrinking the size of the circuits to allow the integrated circuitsto contain more circuit elements and to use less power. As the size ofan integrated circuit critical dimension is reduced and its circuitdensity increases, the critical dimensions of its corresponding maskpattern approaches the resolution limit of the optical exposure toolused in optical lithography. As the critical dimensions of the circuitlayout become smaller and approach the resolution value of the exposuretool, the accurate transcription between the mask pattern and the actualcircuit pattern developed on the resist layer becomes difficult. Tofurther the use of optical lithography to transfer patterns havingfeatures that are smaller than the light wavelength used in the opticallithography process, a process known as optical proximity correction(OPC) has been developed. OPC alters the original layout on the mask tocompensate for distortions caused by effects such as optical diffractionand the optical interaction of features with proximate features. OPCincludes all resolution enhancement technologies performed with areticle.

OPC adds sub-resolution lithographic features to mask patterns to reducedifferences between the original mask pattern, that is, the design, andthe final transferred circuit pattern on the substrate. Thesub-lithographic features interact with the original mask pattern andwith each other and compensate for proximity effects to improve thefinal transferred circuit pattern. One feature that is used to improvethe transfer of the pattern is a sub-resolution assist feature (SRAF).Another feature that is added to improve pattern transference isreferred to as “serifs”. Serifs are small features that can bepositioned on a corner of a pattern to sharpen the corner in the finaltransferred image. As the limits of optical lithography are beingextended far into the sub-wavelength regime, the OPC features must bemade more and more complex in order to compensate for even more subtleinteractions and effects. However, as imaging systems are pushed closerto their limits, the ability to produce reticles with sufficiently fineOPC features becomes critical. Although adding serifs or other OPCfeatures to a mask pattern is advantageous, it also substantiallyincreases the total features count in the mask pattern. For example,adding a serif to each of the corners of a square adds eight morerectangles to a mask or reticle pattern. Adding OPC features is a verylaborious task and requires costly computation time that results in moreexpensive reticles. Not only are OPC patterns complex, but since opticalproximity effects are long range compared to minimum line and spacedimensions, the correct OPC patterns in a given location dependsignificantly on what other geometry is in the neighborhood. Thus, forinstance, a line end will have different size serifs depending on whatis near it on the reticle. This is even through the objective might beto produce exactly the same shape on the wafer. These slight butcritical variations are important and have prevented others from beingable to form reticle patterns. It is conventional to discuss theOPC-decorated patterns to be written on a reticle in terms of mainfeatures, that is features that reflect the design before OPCdecoration, and OPC features, where OPC features might include serifs,jogs, and SRAF. To quantify what is meant by slight variations, atypical slight variation in OPC decoration from neighborhood toneighborhood might be 5% to 80% of a main feature size. Note that forclarity, variations in the design of the OPC are what is beingreferenced. Manufacturing variations, such as line-edge roughness andcorner rounding, will also be present in the actual surface patterns.When these OPC variations produce substantially the same patterns on thewafer what is meant is that the geometry on the wafer is targeted to bethe same within a specified error, which depends on the details of thefunction that that geometry is designed to perform, e.g., a transistoror a wire. Nevertheless, typical specifications are in the 2%-50% of amain feature range. There are numerous manufacturing factors that alsocause variations, but the OPC component of that overall error is oftenin the range just listed.

There are a number of technologies used for forming patterns on areticle, including using optical or particle beam systems. The mostcommonly used system is the variable shape beam (VSB) type, where aprecise electron beam is shaped and steered onto a resist-coated surfaceof the reticle. These shapes are simple shapes, usually limited torectangles of certain minimum and maximum sizes and triangles with theirthree internal angles being 45 degrees, 45 degrees, and 90 degrees ofcertain minimum and maximum sizes. At pre-determined locations, a doseof electrons is shot into the resist of these simple shapes. The totalwriting time for this type of system increases with the number of shots.A second type of system is a character projection system. In this casethere is a stencil in the system that has in it a variety of shapeswhich may be rectilinear, arbitrary-angled linear, circular, annular,part circular, part annular, or arbitrary curvilinear shapes, and may bea connected set of complex shapes or a group of disjointed sets of aconnected set of complex shapes. An electron beam can be shot throughthe stencil to efficiently produce more complex patterns (i.e.,characters) on the reticle. In theory, such a system could be fasterthan an VSB system because it can shoot more complex shapes with eachtime-consuming shot. Thus, an E shot with an VSB system takes fourshots, but could be done with one shot with a character projectionsystem. Note that shaped beam systems can be thought of as a special(simple) case of character projection, where the characters are justsimple characters, usually rectangles or 45-45-90 triangles. It is alsopossible to partially expose a character. This can be done by, forinstance, blocking part of the particle beam. For example, the Edescribed above can be partially exposed as an F or an l, wheredifferent parts of the beam are cut off by an aperture. For a verycomplex reticle, one must fracture the pattern into nearly billions andsometimes approaching trillions of elemental shapes. There are, forinstance, simple rectangular shapes for a VSB system or a limited numberof characters in a character projection system. The more total instancesof elemental shapes (characters) in the pattern, the longer and moreexpensive the write time. However, for writing surfaces such as anOPC-decorated reticle where there are numerous fine variations amongeven the smaller patterns, such projection systems are todayimpractical. The number of characters that can be made available amongwhich the selection of characters by the projection machine takesminimal time is limited, today only allowing about 10-1000 characters.When faced with the plethora of slightly varying OPC patterns that arerequired to be placed on a reticle, no system or method has beenavailable which can accomplish this task.

Thus, it would be advantageous to reduce the time and expense it takesto prepare and manufacture a reticle that is used for a substrate. Moregenerally, it would be advantageous to reduce the time and expense ittakes to prepare and manufacture any surface. It would also be desirableto have a stencil mask that contains some of the complex charactersneeded to produce or generate a surface having various patterns that arerequired to be transferred to a surface. For example, it is possiblethat a surface can have thousands of patterns that have only slightdifferences among each other. In order to prepare a surface it isdesirable to have a stencil mask that can generate many of thesepatterns having slight differences. As discussed more fully herein, thiscan be accomplished by using a stencil mask that contains a set ofcharacters that can be combined, modified, or adjusted to generate thepatterns with many of the slight variations. Thus, there exists a needfor a method and a system for manufacturing a surface that eliminatesthe foregoing problems associated with preparing a surface.

SUMMARY OF THE DISCLOSURE

In one form of the present disclosure, a method for fracturing or maskdata preparation or proximity effect correction is disclosed whichcomprises the steps of inputting patterns to be formed on a surface, asubset of the patterns being slightly different variations of each otherand selecting a set of characters some of which are complex charactersto be used to form the number of patterns, and reducing shot count ortotal write time by use of a character varying technique.

In another form of the present disclosure, a system for fracturing ormask data preparation or proximity effect correction is disclosed whichcomprises a device for inputting patterns to be formed on a surface, thepatterns being slightly different and a device for selecting a set ofcharacters some of which are complex characters to be used to form thenumber of patterns, the set of characters fitting on a stencil mask, andreducing shot count and total write time by use of a character varyingtechnique.

These and other advantages of the present disclosure will becomeapparent after considering the following detailed specification inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cell projection system used to manufacture a surface;

FIG. 2A illustrates a design of a pattern to be placed on a substrate;

FIG. 2B illustrates a pattern formed in a reticle from the design shownin FIG. 2A;

FIG. 2C illustrates a pattern formed in the photoresist of a substrateusing the reticle of FIG. 2B, illustrating that without opticalproximity correction, the image is not nearly similar to the designshown in FIG. 2A;

FIG. 3A illustrates an optical proximity corrected version of thepattern shown in FIG. 2A;

FIG. 3B illustrates an optical proximity corrected version of thepattern shown in FIG. 3A after it is formed in the reticle;

FIG. 3C illustrates a pattern formed in the photoresist of a siliconwafer using the reticle of FIG. 3B;

FIG. 4A illustrates an ideal pattern to be placed on a substrate;

FIG. 4B illustrates two basic stencil shapes;

FIG. 4C illustrates the two basic stencil shapes shown in FIG. 4B in anoverlapping manner;

FIG. 4D illustrates a pattern formed on a reticle by use of theoverlapping stencil shapes shown in FIG. 4C;

FIG. 4E illustrates a pattern formed on a substrate by use of thepattern shown in FIG. 4D;

FIG. 5A illustrates two basic stencil shapes in an overlapping mannerwhere one of the stencil shapes consists of two disjointed squares;

FIG. 5B illustrates a pattern formed on a reticle by use of theoverlapping stencil shapes shown in FIG. 5A;

FIG. 5C illustrates a pattern formed on a substrate by use of thepattern shown in FIG. 5B;

FIG. 6A illustrates a stencil shape for forming a pattern on a reticle;

FIG. 6B illustrates a pattern formed on a reticle by use of the stencilshape shown in FIG. 6A;

FIG. 6C illustrates a pattern formed on a substrate by use of thepattern shown in FIG. 6B;

FIG. 7A illustrates four stencil shapes used to form a pattern on asurface;

FIG. 7B illustrates a pattern formed on a surface by use of the stencilshapes shown in FIG. 7A;

FIG. 8A illustrates a set of characters formed on a stencil mask;

FIG. 8B illustrates a pattern formed on a surface by use of the set ofcharacters shown in FIG. 8A;

FIG. 8C illustrates a set of adjustment characters;

FIG. 8D illustrates by shading, the varying degrees of doses by whicheach character and adjustment characters are exposed in the resist of asurface by use of the set of characters shown in FIG. 8A and theadjustment characters shown in FIG. 8C;

FIG. 8E illustrates a pattern formed in a surface by use of the set ofcharacters shown in FIG. 8A and the adjustment characters shown in FIG.8C;

FIG. 9 illustrates a conceptual flow diagram of how to prepare a surfacefor use in fabricating a substrate such as an integrated circuit on asilicon wafer;

FIG. 10 illustrates another conceptual flow diagram of how to prepare asurface for use in fabricating a substrate such as an integrated circuiton a silicon wafer;

FIG. 11 illustrates a set of characters;

FIG. 12 illustrates a set of characters and adjustment characters withshape variation;

FIG. 13 illustrates a set of characters and adjustment characters withpositional variation;

FIG. 14 illustrates a set of patterns created by shape variation ofadjustment characters;

FIG. 15 illustrates a set of patterns created by various dosage amountsof adjustment characters;

FIG. 16 illustrates a set of patterns created by various dosage amountsof a single character;

FIG. 17 illustrates a set of patterns created by positional variation ofadjustment characters;

FIG. 18 illustrates a conceptual flow diagram of how to prepare asurface for use in fabricating a substrate such as an integrated circuiton a silicon wafer;

FIG. 19 illustrates examples of glyphs; and

FIG. 20 illustrates examples of parameterized glyphs.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like numbers refer to like items,number 10 identifies an embodiment of a lithography system, such as aparticle beam writer system, in this case an electron beam writersystem, that employs character projection to manufacture a surface 12according to the present disclosure. The electron beam writer system 10has an electron beam source 14 that projects an electron beam 16 towardan aperture plate 18. The plate 18 has an aperture 20 formed thereinwhich allows the electron beam 16 to pass. Once the electron beam 16passes through the aperture 20 it is directed or deflected by a systemof lenses (not shown) as electron beam 22 toward another rectangularaperture plate or stencil mask 24. The stencil mask 24 has formedtherein a number of apertures 26 that define various types of characters28. Each character 28 formed in the stencil mask 24 may be used to forma pattern in the surface 12. An electron beam 30 emerges from one of theapertures 26 and is directed onto the surface 12 as a pattern 32. Thesurface 12 is coated with resist (not shown) which reacts with theelectron beam 30. The pattern 32 is drawn by using one shot of theelectron beam system 10. This reduces the overall writing time tocomplete the pattern 32 as compared to using a variable shape beam (VSB)projection system or method. The surface 12 may be a reticle. Thesurface 12 may then be used in another device or machine, such as ascanner, to transfer the pattern 32 onto a silicon wafer to produce anintegrated circuit or a chip. More generally, the reticle 12 is used inanother device or machine to transfer the pattern 32 on to a substrate.

As indicated above, since semiconductor and other nano-technologymanufacturers are reaching the limits of optical lithography it isdifficult to transfer an ideal pattern onto a substrate. For example,FIG. 2A illustrates an ideal pattern 40, which represents a circuit, tobe formed in the resist of a substrate. When a reticle is produced thatattempts to have the pattern 40 formed thereon, the reticle is not aperfect representation of the pattern 40. A pattern 42 that may beformed in a reticle that attempts to represent the pattern 40 is shownin FIG. 2B. The pattern 42 has more rounded and shortened features ascompared to the pattern 40. When the pattern 42 is employed in theoptical lithography process a pattern 44 is formed in the photoresist onthe substrate as depicted in FIG. 2C. The pattern 44 is not very closeto the ideal pattern 40, demonstrating why optical proximity correctionis required.

In an effort to compensate for the difference in the patterns 40 and 44optical proximity correction is used. Optical proximity correctionalters the reticle to compensate for distortions created by opticaldiffraction, optical interactions with neighboring shapes, and resistprocess effects. FIGS. 3A-3C show how optical proximity correction canbe employed to enhance the optical lithography process to develop abetter version of the pattern 44. In particular, FIG. 3A illustrates apattern 50 that is an altered version of the pattern 40. The pattern 50has a serif element 52 added to various corners of the pattern 50 toprovide extra area in an attempt to reduce optical and processingeffects that reduce the sharpness of the corner. When a reticle of thepattern 50 is produced it may appear in the reticle as a pattern 54 asshown in FIG. 3B. When the optical proximity corrected pattern 54 isused in an optical lithography device an output pattern 56, as depictedin FIG. 3C, is produced. The pattern 56 more resembles the ideal pattern40 than the pattern 44 and this is due to optical proximity correction.Although using optical proximity correction is helpful, it may requirethat every pattern be altered or decorated which increases the time andcost to produce a reticle or photomask. Also, the various patternsformed on the reticle may properly have slight differences between themwhen OPC is applied and this adds to the time and expense in preparing areticle. Further, the large number of slight differences or variationsin the patterns may make producing a reticle unmanageable usingcharacter projection systems because the number of required characterswould be too large.

Referring now to FIG. 4A, an ideal pattern 60, such as a contact, thatis to be placed on a substrate is shown. The ideal pattern 60 is in theshape of a square. In an attempt to provide a reticle that will transferthe pattern 60 onto the substrate as closely as possible the followingsteps are used. FIG. 4B shows two basic stencil shapes or characters 62and 64 that can be used to write the ideal pattern 60 onto a reticle.The stencil shape 62 is a square shape 66 having a serif 68 positionedat each corner 70, 72, 74, and 76. The stencil shape 64 is an adjustmentcharacter that may be repositioned on the shape 62 to change or alterthe shape of the serif 68 at one or more of the corners 70, 72, 74, and76. For example, in FIG. 4C the stencil shape 64 is shown overlappingthe corner 74 of the stencil shape 62. When the stencil shapes 62 and 64are used in a cell projection device, such as the electron beam writersystem 10 shown in FIG. 1, to write a pattern onto a reticle, a pattern78 as shown in FIG. 4D will appear. The pattern 78 has a corner 80 thatis more elongated or pronounced that any of the other corners. This isdue to the use of the stencil shape 64 to alter the corner 74. Thepattern 78, which is on a photomask or a reticle, may be used in aconventional lithographic device to transfer the pattern 78 onto asubstrate. For example, if pattern 78 on the reticle was the appropriateshape given the neighboring shapes that affect optical proximitycorrection for producing as close to the pattern 60 as possible on thesubstrate, a pattern 82 as depicted in FIG. 4E, would be the result ofthe pattern 78 being transferred onto a substrate. The pattern 82 issimilar to or an approximation of the ideal pattern 60.

Various other patterns may be formed with the use of the stencil shapes62 and 64. For example, two instances of the shape 64 can be combinedtogether as one character 90 used to overlap the corners 70 and 74 toform a pattern 92, which is shown in FIG. 5A. Stencil shapes 90 and 92are overlapping shots that may produce pattern 94 in FIG. 5B on thereticle. When the pattern 94 on the reticle is the appropriate shapegiven the neighboring shapes that affect optical proximity correctionfor producing as close to the pattern 60 as possible on the substrate, apattern 96 as is shown in FIG. 5C appears on the substrate when thepattern 94 on a reticle is used to project the substrate. The pattern 96is substantially the same as the ideal pattern 60. It is also possibleand contemplated to change or vary the dose that is used in the electronbeam writer system 10, in order to further modify or adjust the variouspatterns that are formed on a reticle. As can be appreciated, with theuse of a few stencil shapes a large number or diversity of shapes can becreated on a surface such as a reticle.

With particular reference now to FIG. 12, a set of sixteen characters,400, 402, 404, 406, 408, 410, 412, 414, 416, 418, 420, 422, 424, 426,428, and 430 are shown as the characters would appear on a surface afterbeing projected by a character projection system. The “0 ear” pattern onthe surface, as shown by the character 400, was projected by a characterwhose design is shown in FIG. 13 as “center CP” 450 to project a patternon a design that is a square as shown in FIG. 13 as “square”. 452. The“2 ears” pattern, as shown by the character 414, is projected by acharacter whose design is shown in FIG. 13 as “ear at 23” 454 and is anexample of an adjustment character. Similarly, the fifteen characters402, 404, 406, 408, 410, 412, 414, 416, 418, 420, 422, 424, 426, 428,and 430 projected in combination with character 400 may create fifteenpatterns 472, 474, 476, 478, 480, 482, 484, 486, 488, 490, 492, 494,496, 498, and 500, as depicted in FIG. 14 on a surface. A pattern 470(FIG. 14) is created by projecting character 400 along with a certaindose. The fifteen patterns 472, 474, 476, 478, 480, 482, 484, 486, 488,490, 492, 494, 496, 498, and 500 of FIG. 14 are glyphs formed by acombination of two character shots that are examples of a largevariation of slightly different patterns that may be generated on thesurface from a small set of characters. A potential reason for the needfor the large variation is optical proximity correction for the eventualprojection using optical lithography in the case where the surface is areticle or a photomask. In order to project the square 452 as shown inFIG. 13 on the substrate, because of the need for optical proximitycorrection, a large variation of slightly different patterns that arevariations of the “O ear” 400 (FIG. 12) need to be generated on thereticle. The present disclosure however is independent of the reason toneed the large variation of slightly different patterns.

By varying the dose of the adjustment characters, the variety ofpatterns that can be shot on the surface through only these charactersfurther increases. FIG. 15 represents the cases 530, 532, 534, 536, and538 of the dose being varied by 0%, −30%, −60%, +50%, and +100%generating critical dimension variations from 10 nm to 19 nm. Inaddition, the dose of the center character represented by “0 ear” 400(FIG. 12) can also be varied to create further variation of slightlydifferent patterns. FIG. 16 represents the different shapes 550, 552,554, 556, and 558 that can be generated on the surface by varying thedose by −40%, −20%, 0%, +25%, and +50%. A shape 560 illustrates theoverlapping of the shapes 550, 552, 554, 556, and 558 to furtherdemonstrate that slightly different patterns can be generated by varyingthe dose. Each of the patterns 550, 552, 554, 556, and 558 may beglyphs, or patterns that are known to be available by combining a smallnumber of character shots. A parameterized glyph may be used as a morecompact representation with more generality to describe a number ofglyphs in a single description. A pattern 560 demonstrates that a doseamount may be a parameter to represent multiple glyphs with onerepresentation. A parameterized glyph that is a single descriptiondescribing all of these possible glyphs 550, 552, 554, 556, and 558 is amore compact and a more flexible representation. Slightly differentpatterns can also be generated by shooting the same basic patterns ofthe adjustment characters in different positions. Referring to FIG. 17,a pattern 580 and a pattern 582 are composed by placing the same 1 earcharacter, such as the character 404 shown in FIG. 12, at differentlocations to the 0 ear character, such as the character 400 in FIG. 12.By preparing a number of variations of the characters, in this case thevariations of the center character and the variations of adjustmentcharacters and varying the dose and relative positions, a very largenumber of slightly different patterns can be projected on the surfacewhile using only two shots. With three or more shots, the number ofavailable glyph patterns that can be projected on the surface increasesgeometrically. Other patterns, such as patterns 584, 586, 588, and 590are also shown in FIG. 17. For example, the pattern 584 is formed bycombining character 400 (FIG. 12) with the character for standarddistance for 2 ears using an adjustment character 432 shown in FIG. 12.The pattern 586 is formed by combining character 400 with the characterfor a long distance for 2 ears using the adjustment character 432 ofFIG. 12. The pattern 588 is formed by combining character 400 of FIG. 12with the character for a standard distance for 3 ears using theadjustment character 424 of FIG. 12. The pattern 590 is formed bycombining character 400 of FIG. 12 with the character for a longdistance for 3 ears using an adjustment character 434 shown in FIG. 12.

With reference now to FIG. 6A, another stencil pattern 100 is shown thatcan be used in an attempt to form a pattern on a substrate, such as asilicon wafer, to resemble the ideal pattern 60 as shown in FIG. 4A. Thestencil pattern 100 includes a stencil shape 102 having a serif 104 ateach corner 106, 108, 110, and 112. The stencil pattern 100 also has asub-resolution assist feature (SRAF) 114 positioned at a diagonal ateach of the corners 106, 108, 110, and 112. The stencil pattern 100 isused to form a pattern 116 on a reticle, as is shown in FIG. 6B. Withreference now to FIG. 6C, the pattern 116 is then used to form a pattern118 on a substrate. The pattern 118 is similar to the ideal pattern 60.

FIG. 7A illustrates four stencil characters 150, 152, 154, and 156 thatmay be used on a stencil mask to be combined to form a sophisticatedshape or pattern 158 on a reticle as shown in FIG. 7B. In particular,the first character 150 is shot or projected onto the reticle, then thesecond character 152 is shot, then the third character 154, and finallythe fourth character 156. The characters are curvilinear in shape andnot rectilinear in shape. In this manner, a complex pattern, such as thepattern 158, may be formed on a reticle. The shapes on the stencil maskmay be termed “characters” and the pattern formed on the reticle may betermed a “glyph”. It is also possible to use dose control in addition toshape variation to generate more slight variations of patterns formed ona reticle by using the same stencil characters, such as the characters150, 152, 154, and 156. A combination of multiple characters may beoverlapped with each other with different dose variations to increasethe variation of possible shapes or patterns that may be generated.Additionally, the position of a character may be changed to increase thevariation of possible shapes or patterns that may be generated. Sincethe shapes of the characters 150, 152, 154, and 156 are curvilinear thisreduces the number of shots that must be used by a particle beam writersystem to shoot or project the characters 150, 152, 154, and 156 onto areticle to write a glyph pattern, such as the pattern 158. For example,the pattern 158 can be shot by using only the four characters 150, 152,154, and 156. While if rectilinear shapes were used many more shots orVSB shots would have to be used. As can be seen, being able to usecharacters instead of VSB shots reduces the time in preparing a reticle.It is also possible to use rectilinear shapes with curvilinear shapes toform a pattern on a reticle. While this feature of character projectionis available in character projection systems for projecting surfacesthat require a very large variety of shapes, the number of charactersthat can be made available as single components are not large enough.The present method and system combines multiple characters with dose,position, or partial projection variations with potentially overlappingshots to increase the number of glyph patterns available dramatically.By having a large number of glyphs as available patterns instead of thevery limited number of characters as available patterns, more complexpatterns can be projected on the surface without significantly affectingthe shot count or write times. Alternatively, using the large number ofthus available glyphs allows surfaces with highly complex shapes to beshot with far less number of shots and write times.

Referring now to FIG. 8A, an example of a set of characters 200 that maybe placed on a stencil mask is shown. The set of characters 200 may beused to form a pattern 202 on a reticle, as is illustrated in FIG. 8B.The pattern 202 may be formed from one or more of the characters in theset of characters 200. However, in an effort to better form an idealpattern to be transferred on a silicon wafer by use of a reticle,adjustment characters or shots 204, as seen in FIG. 8C, may be used tofurther enhance the pattern 202. FIG. 8D depicts an example of thepattern 202 in combination with the adjustment characters 204 that maybe formed in the resist of a reticle. The shading of the adjustmentcharacters 204 indicates a smaller dose for these characters 204 ascompared to the dose used to shoot the other characters 202. FIG. 8Eshows a pattern 206 that is formed in a reticle by use of the set ofcharacters 200 and the adjustment characters 204 with varying doses. Alimited number of characters, such as the set of characters 200, may beused to form a plurality of different shaped patterns or a plurality ofslightly different shaped patterns.

FIG. 9 is a conceptual flow diagram 250 of how to prepare a reticle foruse in fabricating a surface such as an integrated circuit on a siliconwafer. In a first step 252, a physical design, such as a physical designof an integrated circuit is designed. This can include determining thelogic gates, transistors, metal layers, and other items that arerequired to be found in a physical design such as that in an integratedcircuit. Next, in a step 254, optical proximity correction isdetermined. In an embodiment of this disclosure this can include takingas input a library of pre-calculated glyphs or parameterized glyphs.This can also be alternatively, or in addition, include taking an inputa library of pre-designed characters including complex characters thatare to be available on a stencil 260 in a step 262. In an embodiment ofthis disclosure, an OPC step 254 may also include simultaneousoptimization of shot count or write times, and may also include afracturing operation, a shot placement operation, a dose assignmentoperation, or may also include a shot sequence optimization operation,or other mask data preparation operations. Once optical proximitycorrection is completed a mask design is developed in a step 256. Then,in a step 258, a mask data preparation operation which may include afracturing operation, a shot placement operation, a dose assignmentoperation, or a shot sequence optimization may take place. Either of thesteps of the OPC step 254 or of the MDP step 258, or a separate programindependent of these two steps 254 or 258 can include a program fordetermining a limited number of stencil characters that need to bepresent on a stencil or a large number of glyphs or parameterized glyphsthat can be shot on the surface with a small number of shots bycombining characters that need to be present on a stencil with varyingdose, position, and degree of partial exposure to write all or a largepart of the required patterns on a reticle. It is to be understoodthroughout this disclosure that the mask data preparation step 258 ormask data preparation does not include OPC. Combining OPC and any or allof the various operations of mask data preparation in one step iscontemplated in this disclosure. Mask data preparation step 258 whichmay include a fracturing operation may also comprise a pattern matchingoperation to match glyphs to create a mask that matches closely to themask design. Mask data preparation may also comprise inputting patternsto be formed on a surface with the patterns being slightly different,selecting a set of characters to be used to form the number of patterns,the set of characters fitting on a stencil mask, and the set ofcharacters based on varying character dose or varying character positionor applying partial exposure of a character within the set of charactersto reduce the shot count or total write time. A set of slightlydifferent patterns on the surface may be designed to producesubstantially the same pattern on a substrate. Also, the set ofcharacters may be selected from a predetermined set of characters. Inone embodiment of this disclosure, a set of characters available on astencil in a step 270 that may be selected quickly during the maskwriting step 262 may be prepared for a specific mask design. In thatembodiment, once the mask data preparation step 258 is completed, astencil is prepared in a step 260. In another embodiment of thisdisclosure, a stencil is prepared in the step 260 prior to orsimultaneous with the MDP step 258 and may be independent of theparticular mask design. In this embodiment, the characters available inthe step 270 and the stencil layout are designed in step 272 to outputgenerically for many potential mask designs 256 to incorporate slightlydifferent patterns that are likely to be output by a particular OPCprogram 254 or a particular MDP program 258 or particular types ofdesigns that characterizes the physical design 252 such as memories,flash memories, system on chip designs, or particular process technologybeing designed to in physical design 252, or a particular cell libraryused in physical design 252, or any other common characteristics thatmay form different sets of slightly different patterns in mask design256. The stencil can include a set of characters, such as a limitednumber of characters that was determined in the step 258, including aset of adjustment characters. Once the stencil is completed the stencilis used to generate a surface in a mask writer machine, such as anelectron beam writer system. This particular step is identified as astep 262. The electron beam writer system projects a beam of electronsthrough the stencil onto a surface to form patterns in a surface, asshown in a step 264. The completed surface may then be used in anoptical lithography machine, which is shown in a step 266. Finally, in astep 268, a substrate such as a silicon wafer is produced. As has beenpreviously described, in a step 270 characters may be provided to theOPC step 252 or the MDP step 258. The step 270 also provides charactersto a character and stencil design step 272 or a glyph generation step274. The character and stencil design step 272 provides input to thestencil step 260 and to the characters step 270. The glyph generationstep 274 provides information to a glyphs or parameterized glyphs step276. Also, as has been discussed, the glyphs or parameterized glyphsstep 276 provides information to the OPC step 254 or the MDP step 258.

With reference now to FIG. 10, another conceptual flow diagram 300 ofhow to prepare a surface for use in fabricating a substrate such as anintegrated circuit on a silicon wafer is shown. In a first step 302, aphysical design, such as a physical design of an integrated circuit isdesigned. This may be the ideal pattern that the designer wantstransferred onto a substrate. Next, in a step 304, optical proximitycorrection of the ideal pattern generated in the step 302 is determined.This can include selecting glyphs that need to be prepared. Opticalproximity correction may also comprise inputting possible glyphs, theglyphs being based on predetermined characters, and the glyphs beingdetermined using a calculation of varying a character dose or varying acharacter position or applying partial exposure of a character. Further,optical proximity correction may comprise selecting a glyph from thepossible glyphs, computing the patterns on the surface based on theselected glyphs, and selecting another glyph if an error from thecomputation exceeds a predetermined threshold. The predeterminedcharacters may be from a list of geometric patterns. Once opticalproximity correction is completed a mask design is developed in a step304. Then, in a step 306, a mask design is prepared. Once the maskdesign is prepared further enhancement of the mask design takes place ina mask data preparation step 308. The mask data preparation step 308 caninclude a program for determining a limited number of stencil charactersthat need to be present on a stencil to be able to write all of therequired patterns on a reticle. Mask data preparation may also comprisepattern matching to match glyphs to create a mask that matches closelyto the mask design. Iterations, potentially including only one iterationwhere a correct-by-construction “deterministic” calculation isperformed, of pattern matching, dose assignment, and equivalencechecking may also be performed. These steps will assist in preparing anenhanced equivalent mask design. Once the mask is enhanced an equivalentmask design is generated in a step 310. There are two motivations fortests that can be used to determine whether the equivalent mask designis really equivalent to the mask design. One motivation is to pass maskinspection. Another motivation is to confirm that the chip or integratedcircuit will function properly once it has been fabricated. Thecloseness to which a pattern matching operation declares a match may bedetermined by a set of equivalence criteria. An equivalence criteria maybe driven at least partially by litho-equivalence. Litho-equivalence maybe determined by a set of predetermined geometric rules, a set ofmathematical equations that declare a match, a partial match, or a nomatch, or by running a lithography simulation of the pattern on thesurface design and a lithography simulation of a glyph and by comparingthe two results using a set of predetermined geometric rules, or by aset of mathematical equations that declare a match, a partial match, orno match. The MDP step 308 may use a pre-determined set of availablecharacters, glyphs, or parameterized glyphs to optimize for shot countor write time while insuring that a resulting equivalent mask design 310is acceptable to the equivalence criteria. In another embodiment, OPCand MDP may be combined in a correct by construction method, in whichcase there may not be the mask design 306 generated separately from theequivalent mask design 310. The equivalent mask design is used toprepare a stencil as is shown in a step 312. Once the stencil iscompleted the stencil is used to prepare a reticle in a mask writermachine, such as an electron beam writer system. This step is identifiedas a step 314. The electron beam writer system projects a beam ofelectrons through the stencil onto a surface to form patterns in asurface. The surface is completed in a step 316. The completed surfacemay then be used in an optical lithography machine, which is shown in astep 318 to transfer the patterns found on the surface to a substratesuch as a silicon wafer to manufacture an integrated circuit. Finally,in a step 320, a substrate such as a semiconductor wafer is produced. Ashas been previously described, in a step 322 characters may be providedto the OPC step 304 or the MDP step 308. The step 322 also providescharacters to a glyph generation step 326. The character and stencildesign step 324 provides input to the stencil step 312 or to a characterstep 322. The character step 322 may provide input to the character andstencil design step 324. The glyph generation step 326 providesinformation to a glyphs or parameterized glyphs step 328. Also, as hasbeen discussed, the glyphs or parameterized glyphs step 328 providesinformation to either the OPC step 308 or the MDP step 308.

Referring now to FIG. 18, another conceptual flow diagram 700 of how toprepare a surface which is directly written on a substrate such as asilicon wafer is shown. In a first step 702, a physical design, such asa physical design of an integrated circuit is designed. This may be anideal pattern that the designer wants transferred onto a substrate.Next, in a step 704, proximity effect correction (PEC), and other datapreparation (DP) steps are performed to prepare input data to asubstrate writing device, where the result of the physical designcontains multiplicity of patterns that are slightly different. The step704 may also comprise inputting possible glyphs or parameterized glyphsfrom step 724, the glyphs being based on predetermined characters fromstep 718, and the glyphs being determined using a calculation of varyinga character dose or varying a character position or applying partialexposure of a character in glyph generation step 722. The step 704 mayalso comprise pattern matching to match glyphs to create a wafer imagethat matches closely to the physical design created in the step 702.Iterations, potentially including only one iteration where acorrect-by-construction “deterministic” calculation is performed, ofpattern matching, dose assignment, and equivalence checking may also beperformed. A stencil is prepared in a step 708 and is then provided to awafer writer in a step 710. Once the stencil is completed the stencil isused to prepare a wafer in a wafer writer machine, such as an electronbeam writer system. This step is identified as the step 710. Theelectron beam writer system projects a beam of electrons through thestencil onto a surface to form patterns in a surface. The surface iscompleted in a step 712. Further, in a step 718 characters may beprovided to the PEC and Data Prep step 704. The step 718 also providescharacters to a glyph generation step 722. The character and stencildesign step 720 provides input to the stencil step 708 or to a characterstep 718. The character step 718 may provide input to the character andstencil design step 720. The glyph generation step 722 providesinformation to a glyphs or parameterized glyphs step 724. The glyphs orparameterized glyphs step 724 provides information to the PEC and DataPrep step 704. The step 716 may include repeated application as requiredfor each layer of processing, potentially with some processed using themethods described in association with FIGS. 9 and 10, and othersprocessed using the methods outlined above with respect to FIG. 18, orothers produced using any other wafer writing method to produceintegrated circuits on the silicon wafer.

FIG. 11 shows various other basic template shapes or characters 350,352, 354, 356, 358, 360, and 362 that can be used as a set of characterson a stencil to form various patterns on a reticle. The stencilcharacters can be modified slightly by three methods when usingcharacter projection. The first way is to modify the shape and the sizeof the character. For example, variable character projection may be usedwhere a single character can be varied by partially exposing a portionof the character. The second way is to modify the dose amount slightlywhen shooting a given shape and size of a character. A “dose” of aparticle projection shot is the shutter speed, the length of time forwhich a given shot is being projected on the surface of a reticle. “Dosecorrection” is a process step in which the dose amount for any givencharacter projection shot is modified slightly, for example, forproximity effect correction (PEC). In this particular embodiment, inaddition or in combination with other dose correction, the dose isaltered purposefully to slightly modify the size and shape of thecharacters projected onto the surface of a reticle to form patterns orglyphs on the reticle. It is also possible to modify the patterns shotonto a reticle by using multiple overlapping shots of the characters350, 352, 354, and 356, to produce a large variety of patterns orglyphs. The patterns or glyphs may be rectilinear, near-rectilinear,linear, or curvilinear in shape. Further, it is also contemplated tomodify the dose in combination with the use of overlapping characters togenerate even more varieties of patterns or glyphs. Also, a set ofstencil characters may be used with VSB shots, which are an example of asimple character, to form even more patterns or glyphs on a surface. VSBshots and characters may be combined with assigned dose amounts togenerate a large variety of patterns or glyphs. The third method tomodify the stencil characters slightly is with positional variation. Thecharacters 358, 360, and 362 show three variations of positions of thesame character. By varying dose amounts in addition to the geometricshapes of the characters and relative position of the characters withrespect to each other, the number of mask image fragments that can bequickly shot from a given collection of character projection charactersis multiplied. A large number of glyphs that require a small number ofcharacters can be made available to project complex patterns withreduced shot count and write times.

By use of a set of characters, complex shapes including connected orunconnected groups of rectilinear shapes, shapes combining edges ofarbitrary angles, and shapes that include arbitrary curvatures may beformed. Arbitrary curvatures may include circles, semi-circles, andquarter-circles. A set of character projection characters are designedand are included in the stencil installed in a particle beam projectionsystem that writes a reticle. An optical proximity correction system maybe used to select a combination of character projection charactersincluding potentially VSB shots with potential varying dose amounts anddegrees of partial projection to generate a large number of patterns. Aset of characters can be predesigned either specifically for aparticular design or more generally for a set of designs and potentialfuture designs with certain commonalties such as a particularsemiconductor fabrication technology node. The optical proximitycorrection system may fracture overlapping characters each with variabledose amounts. This allows for complex shapes to be created on thereticle.

It is also possible that the optical proximity correction system canstart with a large library of pre-computed or pre-calculated glyphs. Theoptical proximity correction system can then attempt to use theavailable glyphs as much as possible in performing optical proximitycorrection transformation of the original physical design of theintegrated circuit to the reticle design. Glyphs may be each marked withan associated shot count and write time optimization value or values andan optical proximity correction system, a mask data preparation system,or some independent program may optimize for shot count or write time byselecting the lower shot count or write time. This optimization may beperformed in a greedy manner where each glyph is chosen to optimize whatis the best glyph to choose for shot count or write time with a certainorder in which to choose glyphs to match a pattern, or in an iterativeoptimization manner such as with simulated annealing where exchanges ofglyph selection optimizes the overall shot count or write time. It ispossible that some desired patterns to be formed on a reticle may stillremain unmatched by any available glyphs and such patterns may need tobe formed by use of VSB shots.

Referring now to FIG. 19, examples of glyphs 1000, 1002, 1004, and 1006that may be used by optical proximity correction, fracturing, proximityeffect correction, or any other steps of mask data preparation areshown. These glyphs 1000, 1002, 1004, and 1006 may or may not begenerated by a combination of the same characters or they may also beglyphs generated from four different characters. Regardless of themethod of creating the glyphs, the glyphs represent possible patternsthat are known to be possible patterns on the surface that can begenerated with a small number of shots or write times. Each glyph mayhave associated with it the specification for characters required togenerated the glyph, the partial exposure instructions for each of thecharacters, projected required dose of each character, and relativepositions of the characters.

FIG. 20 shows examples of parameterized glyphs 1010 and 1012. The glyph1010 demonstrates a general shape described with a specification of adimension that can be varied, in this case the length X being variedfrom length unit values between 10 and 25. The glyph 1012 demonstratesthe same general shape in a more restrictive way where the length X canonly be one of the specific values, for example, 10, 15, 20, or 25. Theparameterized glyph 1010 demonstrates that these descriptions allow fora large variety of possible glyphs that is not practical with theenumeration method of glyphs that are not parameterized.

An example of a parameterized glyph description for the glyph 1010 maybe as follows:

-   -   pglyph upsideDownLShape (x: nanometers where ((x=10)    -   or((x.>10) and (x<25)) or (x=25)));    -   rect (0, 0, 5, 15);    -   rect (0, 15, x, 20);    -   end pglyph;

An example of a parameterized glyph description for the glyph 1012 maybe as follows:

-   -   pglyph upsideDownLShape2 (x: nanometers where ((x=10)    -   or((x.=15) and (x=20)) or (x=25)));    -   rect (0, 0, 5, 15);    -   rect (0, 15, x, 20);    -   end pglyph;

These example descriptions are based on parameters that a yield logicaltest that determines which values of parameters meet a certain criteriasuch as “where ((x=10) or (x=15) or (x=20) or (x=25)” or “where ((x=10)or ((x>10) and (x<25)) or (x=25).” There are many other ways to describea parameterized glyph. Another example that demonstrates a constructivemethod is as follows:

pglyph upsideDownLShape2 (x : nanometers); glyphFor (x = 10, x + x+5;x>25) { rect (0, 0, 5, 15); rect (0, 15, x, 20); } end pglyph;.

While the specification has been described in detail with respect tospecific embodiments, it will be appreciated that those skilled in theart, upon attaining an understanding of the foregoing, may readilyconceive of alterations to, variations of, and equivalents to theseembodiments. These and other modifications and variations to the presentsystem and method for manufacturing a reticle using character projectionlithography may be practiced by those of ordinary skill in the art,without departing from the spirit and scope of the present subjectmatter, which is more particularly set forth in the appended claims.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tobe limiting. Thus, it is intended that the present subject matter coverssuch modifications and variations as come within the scope of theappended claims and their equivalents.

1. A method for fracturing or mask data preparation or proximity effectcorrection comprising the steps of: inputting patterns to be formed on asurface, a subset of the patterns being slightly different variations ofeach other; and selecting a set of characters some of which are complexcharacters to be used to form the number of patterns; wherein shot countor total write time is reduced by use of a character varying technique.2. The method of claim 1, wherein the slightly different patterns on thesurface produce substantially the same pattern on a substrate.
 3. Themethod of claim 2, wherein an equivalence criteria determines whetherthe patterns on the substrate are substantially the same.
 4. The methodof claim 3, wherein the equivalence criteria is based on lithographysimulation.
 5. The method of claim 1, wherein the set of characters ispredetermined.
 6. The method of claim 5, further comprising the step ofinputting possible glyphs, the glyphs being based on the predeterminedset of characters.
 7. The method of claim 6 wherein the glyphs areparameterized glyphs.
 8. The method of claim 6 further comprising thestep of determining which glyphs to use to match one or more of theinput patterns.
 9. The method of claim 6 further comprising the step ofoptimizing fracturing or mask data preparation or proximity effectcorrection based on shot count or write time.
 10. (canceled) 11.(canceled)
 12. The method of claim 6, wherein the glyphs include subsetsof glyphs and each subset of glyphs includes a multiplicity of slightlydifferent patterns
 13. The method of claim 1, wherein the charactervarying technique is varying character dose.
 14. The method of claim 1,wherein the character varying technique is varying character position.15. The method of claim 1, wherein the character varying technique isapplying partial exposure of a character.
 16. The method of claim 1,wherein the character varying technique is overlapping characters.
 17. Asystem for fracturing or mask data preparation or proximity effectcorrection comprising: a device for inputting patterns to be formed on asurface, a subset of the patterns being slightly different variations ofeach other; and a device for selecting a set of characters some of whichare complex characters, to be used to form the number of patterns;wherein the set of characters fits on a stencil mask, and wherein shotcount or total write time is reduced by use of a character varyingtechnique.
 18. The system of claim 17, wherein the slightly differentpatterns on the surface produce substantially the same pattern on asubstrate.
 19. The system of claim 18 wherein an equivalence criteriadetermines whether the patterns on the substrate are substantially thesame.
 20. The system of claim 19 wherein the equivalence criteria isbased on lithography simulation.
 21. The system of claim 17 furthercomprising a device for inputting possible glyphs and determining whichglyphs to use to match a one or more of the input patterns.
 22. Thesystem of claim 21 further comprising a device for optimizing fracturingor mask data preparation or proximity effect correction based on shotcount or write time.
 23. (canceled)
 24. (canceled)
 25. The system ofclaim 21, wherein the glyphs include subsets of glyphs and each subsetof glyphs includes a multiplicity of slightly different patterns. 26.(canceled)
 27. The system of claim 17, wherein the character varyingtechnique is varying character dose.
 28. The system of claim 17, whereinthe character varying technique is varying character position.
 29. Thesystem of claim 17, wherein the character varying technique is applyingpartial exposure of one of the set of characters.
 30. The system ofclaim 17, wherein the character varying technique is overlappingcharacters.